The ‘memdisk’ arguments are often followed by ‘raw’ in other postings online, however, on my system ‘raw’ caused a quick reboot following the attempted boot.

Documentation of ‘drivemap’ is here . When a usb stick is booted, the bios treats it as (hd0) and the internal disk becomes (hd1). TC expects (hd0) to be the disk which needs to be repaired, so we use ‘drivemap’ to trick it (by swaping the drives).